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P0420 Diagnosis with Freeze Frame Data

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Bryan Holloway, Feb 10, 2016.

  1. Bryan Holloway

    Bryan Holloway Junior Member

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    Location:
    Fullerton, Ca
    Vehicle:
    2006 Prius
    Model:
    II
    I have a 2006 Prius with a little over 200K miles. I get a P0420, after an ECM reset, after about 50-100 miles of driving, and that seems consistent. Im trying to figure out whats going on. Here is the freeze frame data. I was thinking the upstream O2 sensor might be bad as I read O2 sensors should give a value over about 900mv. Just wanted to make sure this is correct before diving in.

    Thanks
     

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  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Most likely, you need to replace the catalytic converter.

    It is true that O2 sensors would produce a lower voltage than the readings shown in your photos. However the first (upstream) sensor is not an O2 sensor. It is an air/fuel ratio sensor and the 3+V reading is normal.
     
    m.wynn likes this.
  3. Bryan Holloway

    Bryan Holloway Junior Member

    Joined:
    Feb 10, 2016
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    4
    1
    Location:
    Fullerton, Ca
    Vehicle:
    2006 Prius
    Model:
    II
    Is there any way to test the cat or know if its bad? No way to judge from the freeze frame data about the cat temperatures? Also I found under "readiness DTC's" I have a P0603, P000A, P0001, P0103. I cleaned the MAF to try and get rid of the P0103. Do the other codes mean anything to you?
     

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  4. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Location:
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    Vehicle:
    2015 Prius
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    Two
    The other three codes are meaningless, and the last one, although a legitimate code, may be meaningless as well since your code reader is giving you bogus results. Get Mini VCI to confirm that P0420 is still present and a legitimate code.

    The engine ECU is testing the catalytic converter on a on-going basis by monitoring the signals provided by the air/fuel ratio sensor and the downstream O2 sensor, while the engine is in closed loop air/fuel ratio control. The air/fuel ratio is swinging up and down while the fuel management is in closed loop, and the air/fuel ratio sensor readings should fluctuate accordingly.

    If you don't believe the results of its testing, which is indicating that the cc is bad, then the only other possibility is that the air/fuel ratio sensor is getting marginal and the voltage swings produced by the sensor are less than the engine ECU would like to see.

    So you can try replacing that sensor first, if you like. Use only the correct Toyota replacement part.
     
    #4 Patrick Wong, Feb 11, 2016
    Last edited: Feb 11, 2016
  5. Bryan Holloway

    Bryan Holloway Junior Member

    Joined:
    Feb 10, 2016
    43
    4
    1
    Location:
    Fullerton, Ca
    Vehicle:
    2006 Prius
    Model:
    II
    Here is a test I found inside of the computer. It says its for the catalyst. And status is LOW. Does this pin the cat to needing a replacement?
     

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